Dual instantaneous envelope tracking

ABSTRACT

Power supply circuitry, which includes a parallel amplifier and a parallel amplifier power supply, is disclosed. The power supply circuitry operates in either an average power tracking mode or an envelope tracking mode. The parallel amplifier power supply provides a parallel amplifier power supply signal. The parallel amplifier regulates an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification. During the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal. During the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application No. 61/812,457 filed Apr. 16, 2013, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to switching power supplies, analog power supplies, and radio frequency (RF) power amplifiers, any or all of which may be used in RF communication systems.

BACKGROUND

As wireless communications technologies evolve, wireless communications systems become increasingly sophisticated. As such, wireless communications protocols continue to expand and change to take advantage of the technological evolution. As a result, to maximize flexibility, many wireless communications devices must be capable of supporting any number of wireless communications protocols, each of which may have certain performance requirements, such as specific out-of-band emissions requirements, linearity requirements, or the like. Further, portable wireless communications devices are typically battery powered and need to be relatively small, and have low cost. As such, to minimize size, cost, and power consumption, RF circuitry in such a device needs to be as simple, small, and efficient as is practical. Thus, there is a need for RF circuitry in a communications device that is low cost, small, simple, and efficient.

SUMMARY

Power supply circuitry, which includes a parallel amplifier and a parallel amplifier power supply, is disclosed according to one embodiment of the present disclosure. The power supply circuitry operates in either an average power tracking mode or an envelope tracking mode. The parallel amplifier power supply provides a parallel amplifier power supply signal. The parallel amplifier regulates an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification. During the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal. During the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal.

In one embodiment of the power supply circuitry, the envelope power supply voltage provides power for amplification to an RF power amplifier, which provides the RF transmit signal. By tracking the RF transmit signal with the envelope power supply voltage, efficiency of the RF power amplifier may be increased. Further, by tracking the envelope power supply control signal with the parallel amplifier power supply signal, efficiency of the power supply circuitry may be increased. This dual tracking is called dual instantaneous envelope tracking.

In one embodiment of the power supply circuitry, to the extent that the parallel amplifier is able to replicate the envelope power supply control signal to provide the envelope power supply voltage, during the envelope tracking mode, a bandwidth of the envelope power supply voltage is about equal to a bandwidth of the envelope power supply control signal. However, the parallel amplifier power supply may have insufficient bandwidth to accurately replicate the envelope power supply control signal to provide the parallel amplifier power supply signal. Therefore, in one embodiment of the parallel amplifier power supply, a bandwidth of the parallel amplifier power supply signal is less than the bandwidth of the envelope power supply control signal.

Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

FIG. 1 shows an RF communications system according to one embodiment of the RF communications system.

FIG. 2 shows the RF communications system according to an alternate embodiment of the RF communications system.

FIG. 3 shows details of an envelope tracking power supply illustrated in FIG. 1 according to one embodiment of the envelope tracking power supply.

FIG. 4 shows details of the envelope tracking power supply illustrated in FIG. 1 according to an alternate embodiment of the envelope tracking power supply.

FIG. 5 shows details of the envelope tracking power supply illustrated in FIG. 1 according to an additional embodiment of the envelope tracking power supply.

FIG. 6 is a graph illustrating communications slots associated with the RF communications system shown in FIG. 1 according to one embodiment of the RF communications system.

FIG. 7 is a graph illustrating an RF transmit signal and an envelope power supply voltage shown in FIGS. 1 and 4, respectively, according to one embodiment of the RF transmit signal and the envelope power supply voltage.

FIGS. 8A and 8B show details of two different embodiments, respectively, of the parallel amplifier power supply illustrated in FIG. 4.

FIG. 9 is a graph illustrating an envelope power supply control signal, a parallel amplifier output signal, and the envelope power supply voltage shown in the envelope tracking power supply illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply.

FIG. 10A is a graph illustrating the envelope power supply control signal shown in the envelope tracking power supply illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply.

FIG. 10B is a graph illustrating the parallel amplifier output signal and a parallel amplifier power supply signal shown in the envelope tracking power supply illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply.

FIG. 11A is a graph illustrating the envelope power supply control signal shown in the envelope tracking power supply illustrated in FIG. 5 according to an alternate embodiment of the envelope tracking power supply.

FIG. 11B is a graph illustrating the parallel amplifier output signal and the parallel amplifier power supply signal shown in the envelope tracking power supply illustrated in FIG. 5 according to an alternate embodiment of the envelope tracking power supply.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

Power supply circuitry, which includes a parallel amplifier and a parallel amplifier power supply, is disclosed according to one embodiment of the present disclosure. The power supply circuitry operates in either an average power tracking mode or an envelope tracking mode. The parallel amplifier power supply provides a parallel amplifier power supply signal. The parallel amplifier regulates an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification. During the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal. During the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal.

In one embodiment of the power supply circuitry, the envelope power supply voltage provides power for amplification to an RF power amplifier, which provides the RF transmit signal. By tracking the RF transmit signal with the envelope power supply voltage, efficiency of the RF power amplifier may be increased. Further, by tracking the envelope power supply control signal with the parallel amplifier power supply signal, efficiency of the power supply circuitry may be increased. This dual tracking is called dual instantaneous envelope tracking.

In one embodiment of the power supply circuitry, to the extent that the parallel amplifier is able to replicate the envelope power supply control signal to provide the envelope power supply voltage, during the envelope tracking mode, a bandwidth of the envelope power supply voltage is about equal to a bandwidth of the envelope power supply control signal. However, the parallel amplifier power supply may have insufficient bandwidth to accurately replicate the envelope power supply control signal to provide the parallel amplifier power supply signal. Therefore, in one embodiment of the parallel amplifier power supply, a bandwidth of the parallel amplifier power supply signal is less than the bandwidth of the envelope power supply control signal.

FIG. 1 shows an RF communications system 10 according to one embodiment of the RF communications system 10. The RF communications system 10 includes RF transmitter circuitry 12, RF system control circuitry 14, RF front-end circuitry 16, an RF antenna 18, and a DC power source 20. The RF transmitter circuitry 12 includes transmitter control circuitry 22, an RF PA 24, an envelope tracking power supply 26, and PA bias circuitry 28.

In one embodiment of the RF communications system 10, the RF front-end circuitry 16 receives via the RF antenna 18, processes, and forwards an RF receive signal RFR to the RF system control circuitry 14. The RF system control circuitry 14 provides an envelope power supply control signal VRMP and a transmitter configuration signal PACS to the transmitter control circuitry 22. The RF system control circuitry 14 provides an RF input signal RFI to the RF PA 24. The DC power source 20 provides a DC source signal VDC to the envelope tracking power supply 26. The DC source signal VDC has a DC source voltage DCV. In one embodiment of the DC power source 20, the DC power source 20 is a battery.

The transmitter control circuitry 22 is coupled to the envelope tracking power supply 26 and to the PA bias circuitry 28. The envelope tracking power supply 26 provides an envelope power supply signal EPS to the RF PA 24 based on the envelope power supply control signal VRMP. The envelope power supply signal EPS has an envelope power supply voltage EPV. The DC source signal VDC provides power to the envelope tracking power supply 26. As such, the envelope power supply signal EPS is based on the DC source signal VDC. The envelope power supply control signal VRMP is representative of a setpoint of the envelope power supply signal EPS. The RF PA 24 receives and amplifies the RF input signal RFI to provide an RF transmit signal RFT using the envelope power supply signal EPS. The envelope power supply signal EPS provides power for amplification. The RF front-end circuitry 16 receives, processes, and transmits the RF transmit signal RFT via the RF antenna 18. In one embodiment of the RF transmitter circuitry 12, the transmitter control circuitry 22 configures the RF transmitter circuitry 12 based on the transmitter configuration signal PACS.

In this regard, in one embodiment of the RF communications system 10, the RF communications system 10 communicates with other RF communications systems (not shown) using multiple communications slots, which may include transmit communications slots, receive communications slots, simultaneous receive and transmit communications slots, or any combination thereof. Such communications slots may utilize the RF transmit signal RFT, the RF receive signal RFR, other RF signals (not shown), or any combination thereof. In one embodiment of an RF communications slot, the RF communications slot is a time period during which RF transmissions, RF receptions, or both, may occur. Adjacent RF communications slots may be separated by slot boundaries, in which RF transmissions, RF receptions, or both, may be prohibited. As a result, during the slot boundaries, the RF communications system 10 may prepare for RF transmissions, RF receptions, or both.

The PA bias circuitry 28 provides a PA bias signal PAB to the RF PA 24. In this regard, the PA bias circuitry 28 biases the RF PA 24 via the PA bias signal PAB. In one embodiment of the PA bias circuitry 28, the PA bias circuitry 28 biases the RF PA 24 based on the transmitter configuration signal PACS. In one embodiment of the RF front-end circuitry 16, the RF front-end circuitry 16 includes at least one RF switch, at least one RF amplifier, at least one RF filter, at least one RF duplexer, at least one RF diplexer, the like, or any combination thereof. In one embodiment of the RF system control circuitry 14, the RF system control circuitry 14 is RF transceiver circuitry, which may include an RF transceiver IC, baseband controller circuitry, the like, or any combination thereof.

FIG. 2 shows the RF communications system 10 according to an alternate embodiment of the RF communications system 10. The RF communications system 10 illustrated in FIG. 2 is similar to the RF communications system 10 illustrated in FIG. 1, except in the RF communications system 10 illustrated in FIG. 2, the RF transmitter circuitry 12 further includes a digital communications interface 30, which is coupled between the transmitter control circuitry 22 and a digital communications bus 32. The digital communications bus 32 is also coupled to the RF system control circuitry 14. As such, the RF system control circuitry 14 provides the envelope power supply control signal VRMP (FIG. 1) and the transmitter configuration signal PACS (FIG. 1) to the transmitter control circuitry 22 via the digital communications bus 32 and the digital communications interface 30.

FIG. 3 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to one embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 includes power supply control circuitry 34, a parallel amplifier 36, and a switching supply 38. The power supply control circuitry 34 is coupled to the transmitter control circuitry 22, the parallel amplifier 36 is coupled to the power supply control circuitry 34, and the switching supply 38 is coupled to the power supply control circuitry 34. The transmitter control circuitry 22 may forward the envelope power supply control signal VRMP to the power supply control circuitry 34.

Since the envelope power supply control signal VRMP is representative of the setpoint of the envelope power supply signal EPS, the power supply control circuitry 34 controls the parallel amplifier 36 and the switching supply 38 based on the setpoint of the envelope power supply signal EPS. The parallel amplifier 36 and the switching supply 38 provide the envelope power supply signal EPS, such that the parallel amplifier 36 partially provides the envelope power supply signal EPS and the switching supply 38 partially provides the envelope power supply signal EPS. The switching supply 38 may provide power more efficiently than the parallel amplifier 36. However, the parallel amplifier 36 may provide the envelope power supply signal EPS more accurately than the switching supply 38. As such, the parallel amplifier 36 regulates the envelope power supply voltage EPV (FIGS. 1 and 7) based on the setpoint of the envelope power supply voltage EPV (FIGS. 1 and 7), and the switching supply 38 operates to drive an output current from the parallel amplifier 36 toward zero to maximize efficiency. In this regard, the parallel amplifier 36 behaves like a voltage source and the switching supply 38 behaves like a current source.

As previously mentioned, in one embodiment of the RF communications system 10, the RF PA 24 receives and amplifies the RF input signal RFI to provide the RF transmit signal RFT using the envelope power supply signal EPS, which provides power for amplification. In one embodiment of the RF input signal RFI, the RF input signal RFI is amplitude modulated. As such, the RF transmit signal RFT is also amplitude modulated, as illustrated in FIG. 7. Since the amplitude of the RF transmit signal RFT is modulated, the amplitude of the RF transmit signal RFT traverses within an envelope of the RF transmit signal RFT. For proper operation of the RF PA 24, the envelope power supply voltage EPV (FIGS. 1 and 7) must be high enough to accommodate the envelope of the RF transmit signal RFT. However, to increase efficiency in the RF PA 24, the envelope power supply voltage EPV (FIGS. 1 and 7) may at least partially track the envelope of the RF transmit signal RFT. This tracking by the envelope power supply voltage EPV is called envelope tracking.

In this regard, since the envelope power supply control signal VRMP is representative of the setpoint of the envelope power supply signal EPS, the envelope power supply control signal VRMP may be received and amplitude modulated to provide at least partial envelope tracking of the RF transmit signal RFT by causing the envelope power supply voltage EPV (FIGS. 1 and 7) to be amplitude modulated.

In a first embodiment of the envelope power supply control signal VRMP, a maximum bandwidth of the envelope power supply control signal VRMP is greater than about 10 megahertz. In a second embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 15 megahertz. In a third embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 20 megahertz. In a fourth embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 20 megahertz. In a fifth embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 25 megahertz. In a sixth embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 35 megahertz. In a seventh embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 45 megahertz. In an eighth embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 55 megahertz. In a ninth embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is greater than about 65 megahertz. In an alternate embodiment of the envelope power supply control signal VRMP, the maximum bandwidth of the envelope power supply control signal VRMP is less than about 500 megahertz.

FIG. 4 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to an alternate embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 4 is similar to the envelope tracking power supply 26 illustrated in FIG. 3, except the envelope tracking power supply 26 illustrated in FIG. 4 further includes a parallel amplifier power supply 40, an offset capacitance voltage control loop 44, an offset capacitive element CA, a first filter capacitive element C1, and a second filter capacitive element C2. Additionally, the switching supply 38 includes switching circuitry 42 and a first inductive element L1. The envelope tracking power supply 26 has an envelope tracking power supply output PSO, such that the envelope power supply signal EPS is provided via the envelope tracking power supply output PSO. As previously mentioned, the envelope power supply signal EPS has the envelope power supply voltage EPV. The parallel amplifier 36 has a feedback input FBI and a parallel amplifier output PAO. The switching circuitry 42 has a switching circuitry output SSO.

In the embodiment shown, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO. In general, the switching circuitry output SSO is coupled to the envelope tracking power supply output PSO via the first inductive element L1. As such, in other embodiments (not shown), the first inductive element L1 is coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO using other intervening elements (not shown).

In the embodiment shown, the offset capacitive element CA is directly coupled between the parallel amplifier output PAO and the envelope tracking power supply output PSO. In general, the parallel amplifier output PAO is coupled to the envelope tracking power supply output PSO via the offset capacitive element CA. As such, in other embodiments (not shown), the offset capacitive element CA is coupled between the parallel amplifier output PAO and the envelope tracking power supply output PSO using other intervening elements (not shown).

In the embodiment shown, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the feedback input FBI. In general, the switching circuitry output SSO is coupled to the feedback input FBI via the first inductive element L1. As such, in other embodiments (not shown), the first inductive element L1 is coupled between the switching circuitry output SSO and the feedback input FBI using other intervening elements (not shown).

In one embodiment of the first filter capacitive element C1, the first filter capacitive element C1 is coupled between the envelope tracking power supply output PSO and a ground. In one embodiment of the second filter capacitive element C2, the second filter capacitive element C2 is coupled between an output from the parallel amplifier power supply 40 and the ground. The parallel amplifier power supply 40 provides a parallel amplifier power supply signal LPS to the parallel amplifier 36 via the output from the parallel amplifier power supply 40. The parallel amplifier power supply signal LPS has a parallel amplifier power supply voltage PSV.

The parallel amplifier 36 receives the parallel amplifier power supply signal LPS and regulates the envelope power supply voltage EPV via the parallel amplifier output PAO based on the setpoint of the envelope power supply voltage EPV using the parallel amplifier power supply signal LPS. As such, the parallel amplifier power supply signal LPS provides power for amplification. In this regard, since the parallel amplifier 36 receives the envelope power supply voltage EPV via the feedback input FBI, the parallel amplifier 36 drives the envelope power supply voltage EPV toward the setpoint of the envelope power supply voltage EPV. In one embodiment of the parallel amplifier 36, during envelope tracking, the parallel amplifier 36 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that the envelope power supply voltage EPV at least partially tracks the RF transmit signal RFT from the RF PA 24.

In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply signal LPS is adjustable on a communications slot-to-communications slot basis. As such, during at least one communications slot 46 (FIG. 6), the parallel amplifier power supply signal LPS is regulated to be about constant. Further, between communications slots 46, 48 (FIG. 6), the parallel amplifier power supply signal LPS may be changed.

An output voltage swing at the parallel amplifier output PAO of the parallel amplifier 36 is approximately between a source headroom voltage SRC (not shown) below the parallel amplifier power supply voltage PSV and a sink headroom voltage SNK (not shown) above the ground. However, during envelope tracking, the envelope power supply voltage EPV may traverse between an expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and an expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. Since the parallel amplifier 36 drives the envelope power supply voltage EPV toward the setpoint of the envelope power supply voltage EPV, the parallel amplifier 36 and the offset capacitive element CA must be able to drive between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. However, the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV may be significantly above ground.

In this regard, without the offset capacitive element CA, the parallel amplifier 36 would need an output voltage swing between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. When the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV is significantly above the ground, the voltage drop between the parallel amplifier output PAO and the ground is large, thereby degrading efficiency. However, by using the offset capacitive element CA, the voltage swing between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV may be shifted down at the parallel amplifier output PAO.

In this regard, to maximize efficiency, the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV at the envelope tracking power supply output PSO would be shifted down to the sink headroom voltage SNK (not shown) above ground at the parallel amplifier output PAO, and the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV at the envelope tracking power supply output PSO would be shifted down to the source headroom voltage SRC (not shown) below the parallel amplifier power supply voltage PSV.

In one embodiment of the offset capacitance voltage control loop 44, the offset capacitive element CA has an offset capacitive voltage OSV, which is regulated by the offset capacitance voltage control loop 44. In one embodiment of the offset capacitance voltage control loop 44, the offset capacitive voltage OSV is adjustable on a communications slot-to-communications slot basis. As such, during at least one communications slot 46 (FIG. 6), the offset capacitive voltage OSV is regulated to be about constant. Further, between communications slots 46, 48 (FIG. 6), the offset capacitive voltage OSV may be changed. Further, in one embodiment of the offset capacitance voltage control loop 44, during at least one communications slot 46 (FIG. 6), the offset capacitive voltage OSV is further regulated, such that an average DC current through the offset capacitive element CA is equal to about zero.

If the offset capacitive voltage OSV is too large, then the parallel amplifier 36 will be unable to drive the parallel amplifier output PAO low enough to provide the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV at the parallel amplifier output PAO. Therefore, in one embodiment of the offset capacitance voltage control loop 44, the offset capacitance voltage control loop 44 regulates the offset capacitive voltage OSV, such that the offset capacitive voltage OSV is less than or equal to a difference between the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV and the sink headroom voltage SNK (not shown). In one embodiment of the sink headroom voltage SNK (not shown), the sink headroom voltage SNK (not shown) is equal to about 0.2 volts. If the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV is represented as EMN, the above requirement is shown in EQ. 1, below. OSV<=EMN−SNK.  EQ. 1

Additionally, the parallel amplifier power supply 40 must make sure that the parallel amplifier power supply voltage PSV is high enough to provide the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV. In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply 40 provides the parallel amplifier power supply voltage PSV, such that the parallel amplifier power supply voltage PSV is greater than or equal to a sum of the source headroom voltage SRC (not shown) and a difference between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the offset capacitive voltage OSV. In one embodiment of the source headroom voltage SRC (not shown), the source headroom voltage SRC (not shown) is equal to about 0.1 volts. If the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV is represented as EMX, the above requirement is shown in EQ. 2, below. PSV>=SRC+EMX−OSV.  EQ. 2

In this regard, in one embodiment of the envelope tracking power supply 26, the offset capacitive voltage OSV is regulated to minimize a voltage drop between the parallel amplifier output PAO and the ground when the parallel amplifier 36 is sinking current. Further, in one embodiment of the envelope tracking power supply 26, the parallel amplifier power supply voltage PSV is regulated to minimize a voltage drop between the parallel amplifier output PAO and the parallel amplifier power supply 40 when the parallel amplifier 36 is sourcing current. Minimizing these voltage drops improves the efficiency of the envelope tracking power supply 26

In one embodiment of the switching supply 38, the switching supply 38 operates to drive an output current from the parallel amplifier 36 toward zero to maximize efficiency. The power supply control circuitry 34 is coupled to each of the parallel amplifier 36, the parallel amplifier power supply 40, the switching circuitry 42, and the offset capacitance voltage control loop 44. As such, in one embodiment of the power supply control circuitry 34, the power supply control circuitry 34 provides information and receives information from any or all of the parallel amplifier 36, the parallel amplifier power supply 40, the switching circuitry 42, and the offset capacitance voltage control loop 44, as needed.

The switching supply 38 and the parallel amplifier power supply 40 receive the DC source signal VDC from the DC power source 20 (FIG. 1). The parallel amplifier power supply 40 provides the parallel amplifier power supply signal LPS based on the DC source signal VDC. The power supply control circuitry 34 provides a parallel amplifier power supply select signal LPSS to the parallel amplifier power supply 40 based on the envelope power supply control signal VRMP. The parallel amplifier power supply 40 provides the parallel amplifier power supply voltage PSV based on the parallel amplifier power supply select signal LPSS, which is based on the envelope power supply control signal VRMP.

In one embodiment of the envelope tracking power supply 26, the envelope tracking power supply 26 operates in one of the envelope tracking mode and the average power tracking mode. Selection of the one of the envelope tracking mode and the average power tracking mode may be made by the RF system control circuitry 14, the transmitter control circuitry 22, or the power supply control circuitry 34. In general, control circuitry selects the one of the envelope tracking mode and the average power tracking mode.

In one embodiment of the envelope tracking power supply 26, the parallel amplifier power supply 40 provides the parallel amplifier power supply signal LPS. The parallel amplifier 36 regulates the envelope power supply voltage EPV based on an envelope power supply control signal VRMP using the parallel amplifier power supply signal LPS, which provides power for amplification. During the envelope tracking mode, the envelope power supply voltage EPV at least partially tracks the envelope of the RF transmit signal RFT and the parallel amplifier power supply signal LPS at least partially tracks the envelope power supply control signal VRMP. During the average power tracking mode, the envelope power supply voltage EPV does not track the envelope of the RF transmit signal RFT.

In one embodiment of the envelope tracking power supply 26, the envelope power supply voltage EPV provides power for amplification to an RF PA 24 (FIG. 1), which provides the RF transmit signal RFT (FIG. 1). By tracking the RF transmit signal RFT (FIG. 1) with the envelope power supply voltage EPV, efficiency of the RF PA 24 (FIG. 1) may be increased. Further, by tracking the envelope power supply control signal VRMP with the parallel amplifier power supply signal LPS, efficiency of the envelope tracking power supply 26 may be increased. This dual tracking is called dual instantaneous envelope tracking.

In one embodiment of the envelope tracking power supply 26, to the extent that the parallel amplifier 36 is able to replicate the envelope power supply control signal VRMP to provide the envelope power supply voltage EPV, during the envelope tracking mode, a bandwidth of the envelope power supply voltage EPV is about equal to a bandwidth of the envelope power supply control signal VRMP. However, the parallel amplifier power supply 40 may have insufficient bandwidth to accurately replicate the envelope power supply control signal VRMP to provide the parallel amplifier power supply signal LPS. Therefore, in one embodiment of the parallel amplifier power supply 40, during the envelope tracking mode, the parallel amplifier power supply signal LPS is modulated and a bandwidth of the parallel amplifier power supply signal LPS is less than the bandwidth of the envelope power supply control signal VRMP.

In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, during at least one communications slot 46 (FIG. 6), the parallel amplifier power supply signal LPS is regulated to be about constant.

FIG. 5 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to an additional embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 5 is similar to the envelope tracking power supply 26 illustrated in FIG. 4, except the switching supply 38 illustrated in FIG. 5 further includes a second inductive element L2. Further, in the envelope tracking power supply 26 illustrated in FIG. 4, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO. However, in the envelope tracking power supply 26 illustrated in FIG. 5, the first inductive element L1 and the second inductive element L2 are coupled in series between the switching circuitry output SSO and the envelope tracking power supply output PSO. As such, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the feedback input FBI, and the second inductive element L2 is directly coupled between the feedback input FBI and the envelope tracking power supply output PSO.

In one embodiment of the envelope tracking power supply 26, the series combination of the first inductive element L1 and the second inductive element L2 form a voltage divider, which provides a phase-shifted signal to the feedback input FBI. The voltage divider may compensate for bandwidth limitations in the parallel amplifier 36, thereby providing improved regulation of the envelope power supply voltage EPV. The first inductive element L1 has a first inductance and the second inductive element L2 has a second inductance.

In a first embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than ten. In a second embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 100. In a third embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 500. In a fourth embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 1000. In a fifth embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is less than 5000.

In one embodiment of the envelope tracking power supply 26, during the envelope tracking mode, the parallel amplifier 36 provides a parallel amplifier output signal PAS based on the envelope power supply control signal VRMP. The parallel amplifier power supply signal LPS has the parallel amplifier power supply voltage PSV, which is high enough to prevent clipping of the parallel amplifier output signal PAS.

FIG. 6 is a graph illustrating multiple communications slots 46, 48 associated with the RF communications system 10 shown in FIG. 1 according to one embodiment of the RF communications system 10. In one embodiment of the RF communications system 10, the RF communications system 10 communicates with other RF communications systems (not shown) using the multiple communications slots 46, 48, which may include transmit communications slots, receive communications slots, simultaneous receive and transmit communications slots, or any combination thereof. The multiple communications slots 46, 48 may utilize the RF transmit signal RFT, the RF receive signal RFR, other RF signals (not shown), or any combination thereof.

The multiple communications slots 46, 48 include a communications slot 46 and an adjacent communications slot 48. In one embodiment of the communications slot 46, the communications slot 46 is a time period during which RF transmissions, RF receptions, or both, may occur. In one embodiment of the communications slot 46 and the adjacent communications slot 48, a slot boundary 50 is between the communications slot 46 and the adjacent communications slot 48. In one embodiment of the slot boundary 50, RF transmissions, RF receptions, or both, may be prohibited. As a result, during the slot boundary 50, the RF communications system 10 may prepare for RF transmissions, RF receptions, or both.

In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply signal LPS may be adjusted during the slot boundary 50 and is prohibited from being adjusted during the communications slot 46 and during the adjacent communications slot 48. In this regard, the parallel amplifier power supply signal LPS is adjustable on a communications slot-to-communications slot basis. Further, in one embodiment of the offset capacitance voltage control loop 44, the offset capacitive voltage OSV may be adjusted during the slot boundary 50 and is prohibited from being adjusted during the communications slot 46 and during the adjacent communications slot 48. In this regard, the offset capacitive voltage OSV is adjustable on a communications slot-to-communications slot basis.

In one embodiment of the offset capacitance voltage control loop 44, to quickly adjust the offset capacitive voltage OSV and since the offset capacitive voltage OSV may be adjusted during the slot boundary 50, a bandwidth of the offset capacitance voltage control loop 44 during the slot boundary 50 is higher than the bandwidth of the offset capacitance voltage control loop 44 during the communications slots 46, 48. In one embodiment of the parallel amplifier power supply 40, during the average power tracking mode, the parallel amplifier power supply signal LPS is adjustable on a communications slot-to-communications slot basis.

FIG. 7 is a graph illustrating the RF transmit signal RFT and the envelope power supply voltage EPV shown in FIGS. 1 and 4, respectively, according to one embodiment of the RF transmit signal RFT and the envelope power supply voltage EPV. During envelope tracking, the envelope tracking power supply 26 operates in the envelope tracking mode. As such, during the envelope tracking mode, the envelope tracking power supply 26 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that the envelope power supply voltage EPV at least partially tracks the RF transmit signal RFT from the RF PA 24, shown in FIG. 7. In this regard, the RF transmit signal RFT is amplitude modulated and the envelope power supply voltage EPV at least partially follows an envelope of the RF transmit signal RFT, as shown. The envelope power supply voltage EPV has the expected maximum 52 and the expected minimum 54, as shown in FIG. 7.

In one embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, the expected maximum 52 of the envelope power supply voltage EPV is high enough to accommodate the envelope of the RF transmit signal RFT without causing significant distortion of the RF transmit signal RFT. In an alternate embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, the expected maximum 52 of the envelope power supply voltage EPV is low enough to cause clipping (not shown) of the envelope of the RF transmit signal RFT, thereby causing some distortion of the RF transmit signal RFT. However, if the distortion of the RF transmit signal RFT is small enough to allow compliance with communications standards, the clipping may be acceptable.

In one embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, during the envelope tracking mode, the expected maximum 52 is approximately aligned with a maximum of the envelope of the RF transmit signal RFT, as shown in FIG. 7. In one embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, the expected minimum 54 is approximately aligned with a minimum of the envelope of the RF transmit signal RFT, as shown in FIG. 7.

During average power tracking, the envelope tracking power supply 26 operates in the average power tracking mode. As such, during the average power tracking mode, the envelope tracking power supply 26 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that during a communications slot 46 (FIG. 6), the envelope power supply voltage EPV is about constant.

FIGS. 8A and 8B show details of two different embodiments, respectively, of the parallel amplifier power supply 40 illustrated in FIG. 4. In general, the parallel amplifier power supply 40 receives the parallel amplifier power supply select signal LPSS and the DC source signal VDC and provides the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. The parallel amplifier power supply signal LPS has the parallel amplifier power supply voltage PSV.

In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply 40 must provide the parallel amplifier power supply signal LPS with enough bandwidth to adequately track the envelope power supply control signal VRMP with the parallel amplifier power supply signal LPS. As such, in one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply 40 is a fast switching power supply. Further, in one embodiment of the parallel amplifier power supply 40, during the envelope tracking mode the parallel amplifier power supply voltage PSV may swing from below the DC source voltage DCV (FIG. 1) to above the DC source voltage DCV (FIG. 1). Therefore, the parallel amplifier power supply 40 must function as both a boost converter and a buck converter.

FIG. 8A shows a first embodiment of the parallel amplifier power supply 40. The parallel amplifier power supply 40 has a two flying capacitor-based charge pump 56, a first flying capacitive element CF1, a second flying capacitive element CF2, and a charge pump inductive element LC. The first flying capacitive element CF1 and the second flying capacitive element CF2 are coupled to the two flying capacitor-based charge pump 56, which charges and discharges each of the first flying capacitive element CF1 and the second flying capacitive element CF2 as needed to provide a needed output voltage to the charge pump inductive element LC. The charge pump inductive element LC is coupled between the two flying capacitor-based charge pump 56 and the second filter capacitive element C2 to provide the parallel amplifier power supply signal LPS.

The two flying capacitor-based charge pump 56 receives power from the DC source signal VDC to provide the parallel amplifier power supply signal LPS. The two flying capacitor-based charge pump 56 receives the parallel amplifier power supply select signal LPSS, which is based on the envelope power supply control signal VRMP (FIG. 4), and provides the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS.

The two flying capacitor-based charge pump 56 provides a switching signal to a low-pass filter, which is formed from the charge pump inductive element LC and the second filter capacitive element C2. The low-pass filter has a first LC time constant. The first LC time constant must be small enough to allow the parallel amplifier power supply 40 to provide enough bandwidth for proper operation.

FIG. 8B shows a second embodiment of the parallel amplifier power supply 40. The parallel amplifier power supply 40 illustrated in FIG. 8B is similar to the parallel amplifier power supply 40 illustrated in FIG. 8A, except the parallel amplifier power supply 40 illustrated in FIG. 8B further includes a first switching element 58 and a third filter capacitive element C3 coupled in series to form a series coupling, which is coupled in parallel with the second filter capacitive element C2.

When the first switching element 58 is in an OPEN state, the low-pass filter is based on only the charge pump inductive element LC and the second filter capacitive element C2, such that the low-pass filter has the first LC time constant. However, when the first switching element 58 is in a CLOSED state, the low-pass filter is based on the charge pump inductive element LC and a parallel combination of the second filter capacitive element C2 and the third filter capacitive element C3, such that the low-pass filter has a second LC time constant, which is longer than the first LC time constant. Operating the parallel amplifier power supply 40 using the second LC time constant may be more efficient than operating the parallel amplifier power supply 40 using the first LC time constant. However, the maximum bandwidth of the parallel amplifier power supply signal LPS when using the second LC time constant is less than the maximum bandwidth of the parallel amplifier power supply signal LPS when using the first LC time constant.

In this regard, in one embodiment of the parallel amplifier power supply 40, during the envelope tracking mode, when a bandwidth of the envelope power supply control signal VRMP is greater than a bandwidth threshold, the parallel amplifier power supply 40 has a first LC time constant. When the bandwidth of the envelope power supply control signal VRMP is less than the bandwidth threshold, the parallel amplifier power supply 40 has a second LC time constant, which is longer than the first LC time constant. As such, during the envelope tracking mode, the parallel amplifier power supply signal LPS is based on low-pass filtering the envelope power supply control signal VRMP (FIG. 4).

FIG. 9 is a graph illustrating the envelope power supply control signal VRMP, the parallel amplifier output signal PAS, and the envelope power supply voltage EPV shown in the envelope tracking power supply 26 illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply 26. The parallel amplifier 36 provides the parallel amplifier output signal PAS based on the envelope power supply control signal VRMP. However, to facilitate processing of the envelope power supply control signal VRMP by the parallel amplifier power supply 40, during the envelope tracking mode, there is a delay 60 between the envelope power supply control signal VRMP and the parallel amplifier output signal PAS such that the parallel amplifier output signal PAS is based on the delay 60 of the envelope power supply control signal VRMP.

Additionally, the offset capacitive voltage OSV allows an output voltage range of the parallel amplifier 36 to be closer to ground. Specifically, the parallel amplifier output signal PAS operates closer to ground than does the envelope power supply voltage EPV. As such, the offset capacitive voltage OSV is the difference between the parallel amplifier output signal PAS and the envelope power supply voltage EPV.

FIG. 10A is a graph illustrating the envelope power supply control signal VRMP shown in the envelope tracking power supply 26 illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply 26. FIG. 10B is a graph illustrating the parallel amplifier output signal PAS and the parallel amplifier power supply signal LPS shown in the envelope tracking power supply 26 illustrated in FIG. 5 according to one embodiment of the envelope tracking power supply 26.

FIG. 10A shows the envelope power supply control signal VRMP illustrated in FIG. 9 according to one embodiment of the envelope power supply control signal VRMP. A slope of the envelope power supply control signal VRMP transitions from a negative slope to a positive slope at a signal valley 62 of the envelope power supply control signal VRMP. The slope of the envelope power supply control signal VRMP transitions from a positive slope to a negative slope at a signal peak 64 of the envelope power supply control signal VRMP.

When the envelope power supply control signal VRMP crosses the signal valley 62, a magnitude of the parallel amplifier power supply signal LPS is held constant for about a signal valley hold time 66 according to one embodiment of the parallel amplifier power supply 40. Upon expiration of the signal valley hold time 66, the parallel amplifier power supply signal LPS generally follows the envelope power supply control signal VRMP as shown in FIG. 10B. The parallel amplifier power supply signal LPS provides sufficient headroom to allow the parallel amplifier 36 to properly provide the parallel amplifier output signal PAS as shown in FIG. 10B. In one embodiment of the signal valley hold time 66, the signal valley hold time 66 is programmable.

When the envelope power supply control signal VRMP crosses the signal peak 64, a magnitude of the parallel amplifier power supply signal LPS is held constant for about a signal peak hold time 68 according to one embodiment of the parallel amplifier power supply 40. Upon expiration of the signal peak hold time 68, the parallel amplifier power supply signal LPS generally follows the envelope power supply control signal VRMP as shown in FIG. 10B. The parallel amplifier power supply signal LPS provides sufficient headroom to allow the parallel amplifier 36 to properly provide the parallel amplifier output signal PAS as shown in FIG. 10B. In one embodiment of the signal peak hold time 68, the signal peak hold time 68 is programmable.

FIG. 11A is a graph illustrating the envelope power supply control signal VRMP shown in the envelope tracking power supply 26 illustrated in FIG. 5 according to an alternate embodiment of the envelope tracking power supply 26. The envelope power supply control signal VRMP illustrated in FIG. 11A is essentially identical to the envelope power supply control signal VRMP illustrated in FIG. 10B.

FIG. 11B is a graph illustrating the parallel amplifier output signal PAS and the parallel amplifier power supply signal LPS shown in the envelope tracking power supply 26 illustrated in FIG. 5 according to an alternate embodiment of the envelope tracking power supply 26.

The parallel amplifier power supply signal LPS illustrated in FIG. 11B is similar to the parallel amplifier power supply signal LPS illustrated in FIG. 11A, except the parallel amplifier power supply signal LPS illustrated in FIG. 11B is based on low-pass filtering the envelope power supply control signal VRMP. The low-pass filtering may be based on filtering characteristics of the parallel amplifier power supply 40, a separate low-pass filter (not shown), or both. The parallel amplifier power supply signal LPS provides sufficient headroom to allow the parallel amplifier 36 to properly provide the parallel amplifier output signal PAS as shown in FIG. 11B.

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow. 

What is claimed is:
 1. Power supply circuitry configured to operate in one of an average power tracking mode and an envelope tracking mode, and comprising: a parallel amplifier power supply configured to provide a parallel amplifier power supply signal; and a parallel amplifier having a parallel amplifier output and configured to regulate an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification, wherein: the parallel amplifier output is coupled to an envelope tracking power supply output via an offset capacitive element; during the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal; and during the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal.
 2. The power supply circuitry of claim 1 wherein during the average power tracking mode and during a communications slot, the parallel amplifier power supply signal is configured to be about constant.
 3. Power supply circuitry configured to operate in one of an average power tracking mode and an envelope tracking mode, and comprising: a parallel amplifier power supply configured to provide a parallel amplifier power supply signal; and a parallel amplifier having a parallel amplifier output and configured to regulate an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification, wherein: during the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal; and during the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal and the parallel amplifier power supply signal is configured to be adjustable on a communications slot-to-communications slot basis.
 4. Power supply circuitry configured to operate in one of an average power tracking mode and an envelope tracking mode, and comprising: a parallel amplifier power supply configured to provide a parallel amplifier power supply signal; and a parallel amplifier having a parallel amplifier output and configured to regulate an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification, wherein: during the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal; the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal; and when a bandwidth of the envelope power supply control signal is greater than a bandwidth threshold, the parallel amplifier power supply has a first LC time constant, and when the bandwidth of the envelope power supply control signal is less than the bandwidth threshold, the parallel amplifier power supply has a second LC time constant, which is longer than the first LC time constant; and during the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal.
 5. The power supply circuitry of claim 1 wherein during the envelope tracking mode, a maximum bandwidth of the envelope power supply control signal is greater than about 25 megahertz.
 6. The power supply circuitry of claim 1 wherein during the envelope tracking mode, a maximum bandwidth of the envelope power supply control signal is greater than about 15 megahertz.
 7. The power supply circuitry of claim 1 wherein during the envelope tracking mode, the parallel amplifier power supply signal is configured to be modulated and a bandwidth of the parallel amplifier power supply signal is configured to be less than a bandwidth of the envelope power supply control signal.
 8. The power supply circuitry of claim 7 wherein during the envelope tracking mode, the parallel amplifier is further configured to provide a parallel amplifier output signal based on the envelope power supply control signal, and the parallel amplifier power supply signal has a parallel amplifier power supply voltage, which is high enough to prevent clipping of the parallel amplifier output signal.
 9. The power supply circuitry of claim 7 wherein during the envelope tracking mode, the parallel amplifier is further configured to provide a parallel amplifier output signal based on the envelope power supply control signal, and the parallel amplifier output signal is based on a delay of the envelope power supply control signal.
 10. The power supply circuitry of claim 7 wherein during the envelope tracking mode, the parallel amplifier power supply signal is based on low pass filtering the envelope power supply control signal.
 11. The power supply circuitry of claim 7 wherein during the envelope tracking mode, when a slope of the envelope power supply control signal transitions from a positive slope to a negative slope, a magnitude of the parallel amplifier power supply signal is held about constant for a signal peak hold time.
 12. The power supply circuitry of claim 11 wherein the signal peak hold time is programmable.
 13. The power supply circuitry of claim 7 wherein during the envelope tracking mode, when a slope of the envelope power supply control signal transitions from a negative slope to a positive slope, a magnitude of the parallel amplifier power supply signal is held about constant for a signal valley hold time.
 14. The power supply circuitry of claim 13 wherein the signal valley hold time is programmable.
 15. The power supply circuitry of claim 1 wherein during at least one communications slot, an average DC current through the offset capacitive element is equal to about zero.
 16. The power supply circuitry of claim 1 further comprising switching circuitry having a switching circuitry output, wherein: the switching circuitry output is coupled to the envelope tracking power supply output via a first inductive element; an envelope tracking power supply has the envelope tracking power supply output and comprises the parallel amplifier, the parallel amplifier power supply, the switching circuitry, the first inductive element, and the offset capacitive element; and the envelope tracking power supply is configured to provide the envelope power supply voltage to an RF power amplifier via the envelope tracking power supply output, such that during the envelope tracking mode, the envelope power supply voltage provides power for amplification to the RF power amplifier.
 17. The power supply circuitry of claim 16 wherein during the average power tracking mode and during a communications slot, the envelope power supply voltage is about constant.
 18. The power supply circuitry of claim 1 wherein the parallel amplifier power supply is further configured to receive a DC source signal from a DC power source, such that the parallel amplifier power supply signal is based on the DC source signal.
 19. The power supply circuitry of claim 18 wherein the DC power source is a battery.
 20. The power supply circuitry of claim 1 wherein the parallel amplifier power supply comprises a two flying capacitor-based charge pump.
 21. The power supply circuitry of claim 1 wherein control circuitry is configured to select the one of the envelope tracking mode and the average power tracking mode.
 22. The power supply circuitry of claim 21 further comprising the control circuitry.
 23. A method comprising: operating in one of an average power tracking mode and an envelope tracking mode; providing a parallel amplifier power supply signal; regulating an envelope power supply voltage based on an envelope power supply control signal using the parallel amplifier power supply signal, which provides power for amplification; during the envelope tracking mode, the envelope power supply voltage at least partially tracks an envelope of an RF transmit signal and the parallel amplifier power supply signal at least partially tracks the envelope power supply control signal; and during the average power tracking mode, the envelope power supply voltage does not track the envelope of the RF transmit signal and the parallel amplifier power supply signal is configured to be adjustable on a communications slot-to-communications slot basis. 